Another suggestion is Carnitine helps the body turn fat into energy and decrease fatigue. I do take it.

“The coronavirus disease is a viral infection that could induce different respiratory, gastrointestinal, and vascular problems. Evidence shows that many patients with the disease experience a long recovery period, and symptoms such as fatigue persist for several months after infection.

Fatigue depends on a variety of conditional and physiological factors, and its exact molecular mechanism has not yet been elucidated; however, it is probably caused by cytokine storm, which can cause inflammation and anorexia, followed by muscle loss, weakness, and tiredness.

L-Carnitine is a trimethylated amino acid that is structurally similar to choline and is needed as a cofactor to convert long-chain free fatty acids to acylcarnitine and transfer them to the mitochondrial matrix.
Dietary L-carnitine supplementation successfully has beneficial effects on the energy metabolism of the cells and related mechanisms in regeneration of muscles.

Since the beneficial effects of this medication in relieving fatigue caused by diseases such as cancer, MS, etc. have been demonstrated, it can also be considered as a potential option for relieving the fatigue caused by COVID-19. “
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8667465/

Did the doctors test your B12 and folate levels? A decade ago I had a B2 deficiency and couldn't walk. I have been taking sublingual B12 (under the tongue liquid) and I have been fine. I also have a lot of lentils that are high in folate. Both deficiencies can cause anemia that impacts the ability of the red blood cells to carry oxygen.